1. Field of the Invention
The present disclosure relates to a door locking device of a distribution board of an air circuit breaker, and particularly, to a door locking device of a distribution board of an air circuit breaker, allowing a door of the distribution board to be opened only in a disconnection state.
2. Background of the Invention
In general, a circuit breaker is an electric device for switching (or opening and closing a load or breaking a circuit when an accident such as a short-circuit occurs or in the case of earthing in transmission and transformation of electric power or in an electric circuit. Among circuit breakers, an air circuit breaker uses air as an arc-extinguishing medium and is largely used in a low voltage device.
An air circuit breaker may be classified as a fixed type air circuit breaker fixed to and used in a distribution board or any other locations and a withdrawable type air circuit breaker in which a circuit breaker body thereof is installed to be drawn in and out from a cradle. The withdrawable type air circuit breaker is advantageous for maintenance of the circuit breaker body so as to be frequently used.
According to relative positions between a circuit breaker body and a cradle, the withdrawable type air circuit breaker may enter three positions (states), that is, a disconnection position (state) in which the circuit breaker body is drawn out from the cradle and a control (power) terminal is completely separated, a test position (state) in which the circuit breaker body is drawn into the cradle by a predetermined distance and a control terminal is electrically connected so that a connection state of the circuit breaker may be checked, and a connection position (state) in which the circuit breaker body is completely drawn in the cradle and a main circuit terminal is connected so that a main circuit is conducted.
FIGS. 1 and 2 illustrate a door locking device of a circuit breaker according to a related art. The related art is a technique disclosed in the Korean Patent Registration No. 10-1345173 entitled “Device for connecting circuit breaker and distribution board door”.
The related art provides a device for connecting a circuit breaker and a distribution board door, operating not to allow opening of the distribution board door for electrical safety when the circuit breaker received in a distribution board is in a closing position (or ON position or conduction position). The device includes a main shaft 1, a main shaft lever 2, a first interworking lever mechanism 110, a second interworking lever mechanism 120, power transmission units E, W1, W2, and W3, and a constraint plate 130.
The first interworking lever mechanism 110 is installed on an outer side of the circuit breaker CB and connected to the main shaft lever 2 so as to be rotatable cooperatively according to rotation of the main shaft lever 2. The first interworking lever mechanism includes a first board 7 and a first lever 3. The first lever 3 is rotatably supported by the first board 7 through a first rotational shaft 4 installed to penetrate through the first board 7 and transmits power based on rotation of the main shaft lever 2 to the power transmission units E, W1, W2, and W3. A connection recess portion 3a1 of the first lever 3 may be coupled to a connection protrusion portion 2a of the main shaft lever 2, and thus, the first lever 3 may make seesaw movement centered on a first rotational shaft 4 according to rotation of the main shaft lever 2. A support bolt 5 placed below the first lever 3 supports a lower surface of the first lever 3.
When an end head portion E ascends or descends together with a support cap 6 according to the seesaw movement of the first lever 3, a first wire end portion W2 and a second wire end portion W3 integrally connected to the end head portion E may be pulled or pushed.
The second interworking lever mechanism 120 may be installed on an inner wall surface of a distribution board enclosure 140 and connected to the first interworking lever mechanism 110 by a power transmission unit (wire), whereby the second interworking lever mechanism 120 may rotate to a locking position in which opening of the distribution board door 141 is not permitted and to a release position in which opening of the distribution board door 141 is permitted according to rotation of the main shaft 1 to a circuit opening position or to a circuit closing position. The second interworking lever mechanism 120 may include a second board 121 and a second lever 122.
The second lever 122 is rotatably coupled to a second rotational shaft 123 supported by the second board 121 and includes a hook portion 122a, a spring connection portion 122b, and a power transmission unit connection portion 122c. 
A force generated by the first lever 3 and transmitted through the power transmission unit pushes or pulls the power transmission unit connection portion 122c to allow the hook portion 122a to be caught to or released from the constraint plate 130, thus restraining or releasing opening of the distribution board door 141.
However, as described above, the distribution board door locking device of the air circuit breaker according to the related art has a complicated structure, increasing production cost and maintenance cost, and since it includes a large number of connection elements, there is a high possibility of a defective operation.